1. Field of the invention
The present invention relates to a method and a device for determining the orientation of any solid body within a given space.
Numerous systems need to know, in practically real time, how the parameters of orientation of a solid within a given reference frame are changing, and to be able to track this change. This is notably the case of visor systems mounted on the actual headsets of aircraft and helicopter pilots, enabling them to see the image of a grating which is projected at infinity and superimposed on outside scenes. It is absolutely essential that the images received by the pilot always correspond to the coordinate system of the carrier (aircraft, helicopter etc.) regardless of movements of the headset with respect thereto, so as to be able to indicate, for example, a lined-up target to a weaponry system.
2. Prior art
The use of an electromagnetic position and orientation detector is known which comprises, firstly, a transmitter having a fixed position in the given coordinate system comprising three windings that are each energised in turn by a generator and, secondly, a sensor fixed to the solid and also consisting of three windings whereby for each position of the solid, there are nine corresponding signals induced by the windings of the transmitter, these nine signals enabling the position and orientation of the solid to be calculated. However, the electromagnetic fields set up or induced can suffer considerable interference as the result of the presence of metallic elements in the surroundings, and such a detector requires either the use of auxiliary means to supply a reference signal for correction purposes (French patent 2,655,415), or the use of a preliminary phase in which modelling is performed to take account of such interference.
Electro-optical systems also exist which involve placing a certain number of marks on the solid which can be emitting or non-emitting point or surface marks, their position in a coordinate system R.sub.s bound to the solid being well known, after which, using optical detectors fixed in the coordinate system R.sub.o of the measurement space, the position of a certain number of straight lines or curves which link at least two separate marks of the solid are located. It can be shown that the errors in measurement of the solid's orientation parameters is on the one hand proportional to the uncertainty regarding measurement of the position of the marks in the coordinate system R.sub.o, and, on the other hand, inversely proportional to the distance that separates these marks. Such systems are hence better suited to solids of appreciable size for which there can be a large spacing between the marks, but the measurements still make it necessary to calculate the position of at least two points on the solid.